Method of removing nickel and cobalt impurities from zinc electrolyte solutions



Patented May 30, 1950 --2,509,91-c ME'TI'IGD *o'F REMOVING NIckEI; AN'D oo- YBALTIMPURITIES FROM ZINO-EL'ECTRO- LYTE SOLUTIONS Dinsmore l aurenceGriffith and Mavis-JeanRankin FlinFlon,Manitoba, Canada, assignors to Hudson Bay Mining and Smelting- 00., Limited,

"UNITED TATE'S LPATEENT OFF-I'CJE.

Winnipeg, Manitoba, Canada "No-Drawing. Application March 5,1946, Serial No. 652,244

tonnes. (ores- 125) This invention relates to the removal of 'impuritiespresent in zinc electrolyte solutions priorto the'recovery of zinc therefrom by the electrolytic method, and it is directed particu- 'larly to the remo'val'of cobalt and nickel from i such solutions.

It is well known that impurities inthee'lectro- 'lyte cause .great difiiculty during the operation of plating by electrical mthodsjin some cases due to the impurity itself. plating and so causing the" deposit tobeimpureand ofless value, and

that such a displacement may be aided by the .presence of a metal low in the electromotive series. Thus it is commonjafter iron and other metals have been precipitated by treating an electrolyte with zinc oxide or roasted zinc ore or lime while air is blown through'the solution,

to treat it with zinc dust-and to-increasethe purifying action of the Zinc dust by "coating it with finely divided copper. commonly formed by precipitating it from the solution to be purified by the zinc dust.

On the basis of the above generalization as to removal of one metal in solution by another metal higher in the electromotive series, and this removal being aided by the presence of a metal low in the electromotive series, one would expect that all of the impurities could be removed without serious difficulties. Experiments have shown, however, that certain elements such as cobalt and nickel, which should, from the position assigned to them in the electromotive series, easily be removed, are exceedingly difiicult to precipitate, the difficulty becoming more pronounced as the quantity of the impurities present in the electrolyte becomes less. Thus, it has not been possible to remove more than a few milligrams per litre, say from about down to about 10 milligrams per litre, of such impurities as cobalt and nickel, and much work has been done to determine methods of removing these and other impurities which are similarly diflicult to precipitate.

It has been proposed to use arsenic with zinc dust and copper but we have found that zinc dust, copper and arsenic additions alone are of :little, if any, value in removing impurities such as cobalt and nickel and this is illustrated-by the following experiment which was carried out witha sample of tankhouse electrolyte (electrp- 1 lyte ready for electrolysis in the hydrometallurgical process for winning zinc) having the followinganalysis:

Zinc "grams perlitre, about" 120 0 :Copper "mini'grar'ns 'per'li'tre "0.4.

T5 Zinc dust and copper were then added tothi's electrolyte, using the normal small amounts,

namely, 5grams per litre of zinc dust and 1.4 grams per litre of copper as copper sulphate.

Then purification tests were run on samples or this electrolyte with additions of arsenic (as'ars'nious oxide dis'solve'd in sodium hydroxide and water, and neutralized to methyl orange with sulphuric acid) "as set forth below, the samples beingagitated foronehour at 45 C. The an- 25 alyses of the filtrates from these tests were=as follows:

Analylslixsnof treated siil'htion in igrams pcr ire This copper is 30 Test Extra Additions Cu Cd 00 As Sb 0.5 0.2 11.0 .5 0.022 B 0.6 0.2 12.0 1.5 0.026 O 200 mgJLArsenic 0.7 0.2 12.6 8.0 0.024 35 D 300mg./1. Arsenic 4.5 0.3 12.9 20.0 0.028

We have discovered that surprisingly good results are obtained in the removal of impurities and particularly cobalt if small amounts of both thallium and arsenic in the form of soluble compounds are present in addition to the normal small amounts of zinc dust and a soluble copper compound. The amount of thallium to be added varies according to the concentration of impurities in the particular electrolyte to be purified, and precise directions as to the addition required fora given degree of purification may, therefore, not be stated. However, tests made on samples of tankhouse electrolyte show that remarkably good results are obtained with as little as ten milligrams per litre of thallium and that about twenty-five milligrams per litre is usually sufiicient to reduce cobalt and nickel present as impurities to vary small amounts.

Thus, for example, 25 milligrams per litre of Cu Cd Sb Similarly, 25 milligrams per litre of thallium, as thallium sulphate, with 175 milligrams per litre of arsenic in sulphuric acid solution made nickel not detectable in a sample of tankhouse electrolyte of the following analysis:

Zinc grams per litre 135 Cadmium "milligrams per litre 0.4 Antimony do 0.02 Copper -do 0.5 Arsenic do 0.02 Cobalt do 23.6 Nickel do 18.8

The additions of zinc dust and copper were as set forth above and, after agitation for one hour at 40 C., the analysis of the filtrate was:

Nickel Not detectable Cobalt milligrams per litre 1.2

The considerable eifect of the thallium addition is apparent on comparing the above analysis with the following result of a corresponding test carried out on the same electrolyte without any addition of thallium. The analysis was:

Milligrams per litre Nickel 13.6 Cobalt 18.0

Other tests carried out showed that bismuth, gold, iron, cadmium, mercury, chromium, molybdenum, phosphorus, gallium, tungsten, sulphur, tellurium, germanium, selenium, nickel, palladium and platinum are, amongst others, of no value along with zinc dust, copper and arsenic; indeed certain of these metals, as for example platinum, are very detrimental, since not only is cobalt not removed, but the solution is left high in copper and arsenic.

What we claim as our invention is:

1. A method of removing impurities from zinc electrolyte solutions, comprising contacting the electrolyte with small amounts of zinc dust, in the presence of small amounts of soluble copper, arsenic and thallium compounds.

2. A method of removing impurities from zinc electrolyte solutions, comprising contacting the electrolyte with small amount of zinc dust in the'presence of small amounts of soluble copper and arsenic compounds and from about 10 to about 25 milligrams per litre of thallium in the form of a soluble compound.

3. A method of removing impurities from zinc electrolyte solutions, comprising adding to the electrolyte small amounts of zinc dust, copper sulphate, a soluble arsenic compound, and thallium sulphate.

4. A method of removing impurities from zinc electrolyte solutions, comprising adding to the electrolyte small amounts of zinc dust, copper sulphate, a soluble arsenic compound, and from about 10 to about 25 milligrams per litre of thallium sulphate.

DINSMORE LAURENCE GRIFFITH. MAVIS JEAN RANKIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,733,676 Stevens et al. Oct. 29, 1929 2,396,569 Griffith et al. Mar. 12, 1946 OTHER REFERENCES Mellors Comprehensive Treatise on Inorganic Chemistry," 1924, vol. 5, page 407, published by Longmans, Green & Co. 

3. A METHOD OF REMOVING IMPURITIES FROM ZINC ELECTROLYTE SOLUTIONS, COMPRISING ADDING TO THE ELECTROLYTE SMALL AMOUNTS OF ZINC DUST, COPPER SULPHATE, A SOLUBLE ARSENIC COMPOUND, AND THALLIUM SULPHATE. 